Results 1 to 5 of 5

Thread: Long Term Spark Trims? What Happens When Timing is Pulled Due to Knock?

  1. #1
    Lifetime Member
    Join Date
    Mar 2009
    Posts
    746

    Default Long Term Spark Trims? What Happens When Timing is Pulled Due to Knock?

    I know the 411 will interpolate between the 2 maps, does it have long term trims? Reason I ask is I pulled to a lower elevation, then fired up the scan tool to get some data. I only logged KR, didn't log any of the other parameters where it'll pull timing. I opened the throttle to atmospheric locked in 4th and it began to pull around 5 degrees of timing. It did this for a while, then slowly dropped to 4, then 3, then 2, 1, and then none and stayed at 0 KR after that. Was the PCM trimming timing back to a happier spot? The truck never accelerated much during that ordeal as it had 8500# behind it so the load and RPM were kept constant. Once it read 0 KR after that, I figured I was good to go but now I'm wondering if it saved itself from me. I want the timing on the upper end, but I don't want any KR and I'd never hit these load cells with the current tune either.
    1998 GMC Sierra K1500 5.7/4L80E, longtubes, 411 w/COS 5, marine cam/intake, Whipple. 91 octane at 6000'.
    1997 GMC Sierra K3500 7.4/4L80E, 411 w/COS 3, Whipple, small cam.
    2004 Corvette Z06 with longtubes.

  2. #2
    Joe (Moderator) joecar's Avatar
    Join Date
    Apr 2003
    Posts
    28,405

    Default

    Was it running from the LO spark table, and then slowly sliding back up to the HO spark table...?

  3. #3
    Lifetime Member
    Join Date
    Mar 2009
    Posts
    746

    Default

    I'm not sure, nor do I know how to check for that. I have the logs at home. My guess was that it was running the HO spark table then dropped somewhere in between. Will it permanently stay in between? Is there a foolproof way to check for that? I always figured if there was no KR, then I was good to go. I always see a couple isolated incidents of KR in my logs, but since they're not persistent I've written them off. Now I'm thinking the reason they're not persistent may be because the PCM is interpolating between the 2 maps.
    1998 GMC Sierra K1500 5.7/4L80E, longtubes, 411 w/COS 5, marine cam/intake, Whipple. 91 octane at 6000'.
    1997 GMC Sierra K3500 7.4/4L80E, 411 w/COS 3, Whipple, small cam.
    2004 Corvette Z06 with longtubes.

  4. #4
    Joe (Moderator) joecar's Avatar
    Join Date
    Apr 2003
    Posts
    28,405

    Default

    It should slowly slide back to the HO table (unless knock persists).

    Yes, sliding between HO/LO maps = interpolating between HO/LO maps.

    To check this, you could use the scantool->tunetool link pid highlighting...

    post log and tune files.

  5. #5
    Lifetime Member
    Join Date
    Mar 2009
    Posts
    746

    Default

    Sorry for the delayed response, I've been out of town a while. Below is the tune and a log from that tune when I was pulling my trailer in the middle of KS. This one had the most knock activity, but I think one of the longer ones captured the KR when it was locked in 4th. This one appears to have captured knock from 3rd gear. The fact that it's there and then gone is what really throws me.

    Log_0000.efi
    411 Efan Take 1.tun
    1998 GMC Sierra K1500 5.7/4L80E, longtubes, 411 w/COS 5, marine cam/intake, Whipple. 91 octane at 6000'.
    1997 GMC Sierra K3500 7.4/4L80E, 411 w/COS 3, Whipple, small cam.
    2004 Corvette Z06 with longtubes.

Similar Threads

  1. Short/Long Term Fuel Trims...do these look ok?
    By kjlindgr in forum E37, E38 & E67 PFI ECM's
    Replies: 18
    Last Post: November 21st, 2014, 03:23 PM
  2. How to reset long term fuel trims?
    By Hulkss in forum Gen IV V8 Specific
    Replies: 11
    Last Post: November 8th, 2010, 05:25 AM
  3. Long Term fuel Trims..
    By waterbug1999 in forum Gen III V8 Specific
    Replies: 52
    Last Post: July 25th, 2009, 04:23 PM
  4. Long term fuel trims issues
    By Kurtomac in forum General (Petrol, Gas, Ethanol)
    Replies: 21
    Last Post: August 7th, 2008, 06:08 AM
  5. Long Term Trims
    By oztracktuning in forum Custom Operating Systems
    Replies: 15
    Last Post: July 6th, 2006, 12:20 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •